@waynewiz can you post a screen shot (Cmd-Shift-4) with the context of your colour picker selection?

I assume you are clicking on the PoserSurface node's Diffuse_Color colour chip and seeing the Poser colour picker come up first? When you hover your cursor over the saturated or pastel rainbow pickers below the text, you should see the second square at the top match the colour the cursor is over (doesn't work in a screen region capture as you have to move the mouse away). If you subsequently click on the RGB square at the top right, only then do you get the macOS System Colour Picker. which allows you to choose which selection mode you want.

@waynewiz ah, I see you're in the Simple shader tab, rather than the Advanced tab that I was choosing from. Do you still get the System Colour picker if you click on the square with red, green and blue vertical bands to the right of the "Select a Color" text?